John Richardson of the Shark Trust said: "They are predominantly an oceanic, open water species, and not commonly found close to shore.

5

Blue sharks have been known to attack humans but they could hardly be described as frequent 'man-eaters'Credit: Alamy

5

The last unprovoked blue shark attack in British waters was in 1847Credit: Alamy

''But it is certainly not unprecedented to see one in such shallow waters.

"To see a free-swimming blue shark close to shore like this is a real privilege.

“If this shark remains in St Ives harbour, the Shark Trust advises people to give it plenty of space until it moves back offshore to its usual habitat.

"Due to the confined nature of the harbour, which could hinder the shark’s ability to naturally move away from disturbance, the trust strongly advises people not to get into the water with the shark.
“We can only speculate on why this shark has come so close to shore.

"Possible explanations include injury or illness, or perhaps disorientation after following prey inshore. But this is speculation only."

Blue sharks in British waters

Blue sharks have been known to go for humans and for boats out in sea and are therefore classified as a "dangerous" species.

There are also reports of attacks following air or sea disasters with accounts suggesting shipwrecked sailors have been maimed by them.

Blue sharks have been reported to circle swimmers or divers for 15 minutes or more before going in for a bite.

The beasts are described as "not overly aggressive" but should be approached with caution, as they may attempt a "test bite".

DEATH TOLL RISES

HOSPITAL THIEF

BABY PANIC

'World's oldest mum', 74, in intensive care along with husband, 78, after birth

Mr Simmonds, of Llanelli, said: "It's so rare and difficult to land a thresher shark as they are so large. In the shark world, it's up there at the top of the list.

"It was so big it got caught in the hatch door of the boat as we tried to get it on board.

"The body was 6ft 8in long and the tail was 6ft - it was the length of the boat.

We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368 . You can WhatsApp us on 07810 791 502. We pay for videos too. Click here to upload yours.